Interactive effects of psyllium husk and grape seed tannins in starch-based systems for modulating digestibility

Starch is a versatile carbohydrate whose properties get influenced upon interaction with other biomolecules within the food matrix. The incorporation of bioactive compounds (tannins) and dietary fiber could modify starch properties. This study investigated the effect of psyllium husk fiber (5% and 10%) and grape seed tannins (0.5%), alone and in combination, on the pasting, textural, structural, antioxidant, and in-vitro digestibility properties of corn starch. RVA analysis showed that psyllium-containing systems exhibited substantially higher viscosity and lower apparent pasting temperature than corn starch, while the effect of tannins depended on fiber concentration. Fiber increased firmness, whereas tannins modified firmness and consistency differently at 5% and 10% fiber. Particle size analysis showed larger apparent particle sizes and greater structural heterogeneity following fiber incorporation, with tannins further modifying the distribution. Starch-iodine binding decreased in fiber-only complexes, indicating reduced accessibility of amylose helices, whereas tannins partly restored iodine-binding responses in the fiber-containing systems. FT-IR spectra showed no new bands, while shifts in characteristic regions were consistent with changes in hydrogen-bonding environments and other non-covalent associations. Tannin-containing systems showed markedly higher antioxidant activity, with T>F5T>F10T in both FRAP and ABTS assays. Fiber and tannins significantly modified starch digestibility, with F5T and F10T showing the lowest RDS and highest RS contents. Two-way ANOVA confirmed significant fiber x tannin interactions for RDS, SDS, and RS, while additive-effect analysis showed departures from simple additivity. Overall, psyllium and tannins interactively modified starch functionality and digestibility, supporting their potential application in starch-based functional food systems.